Astronomy190 - Topics in Astronomy Astronomy and Astrobiology Lecture 4 : Astronomy Basics Ty Robinson

Questions of the Day What does it mean to say that we are made of star stuff? What are Kepler’s three laws? What is spectroscopy and how does it help us to learn about the Universe?

Copernican Revolution Earth is not at the center of the Universe. Nikolaus Copernicus ( )

100,000 light years speed of light = 180,000 miles/second ~300 billion stars

Question There are roughly 100 billion (=1x10 11 ) galaxies in the observable Universe. If there are about 300 billion (=3x10 11 ) stars in every galaxy, how many stars are there in the observable Universe? Answer: 3x10 22 stars = 30 billion trillion What if each star has one Earth-like planet? 4x x x10 11 infinite

Composition of the Interstellar Material

Orion Nebula ~3 light years ~3,000 stars light years

Star Cluster ~2 light years Question The stars in this cluster are all at the same distance from Earth. What are two key features of stars that we can deduce from looking at the stars in this image?

Hertzsprung-Russell (HR) Diagram Luminosity Color (type) Mass Size Lifetime

Question If it takes about 1 billion (=10 9 ) years for simple life to originate and flourish on a planet, what types of stars (OBAFGKM) are good places to search for life? all stars OBA G FGKM

Low Mass (FGKM) Stars E=mc 2

All good things must come to an end…

Planetary Nebula ~1 light year Question If this were the whole picture, would we be here today? Why?

High Mass (OBA) Stars Question If this were the whole picture, would we be here today? Why? Note: Nitrogen is a product of Helium fusion.

Supernova The energy released during a supernova is equal to the entire energy that the Sun will release in its entire life!

Planet Formation Jupiter’s Orbit dust m boulder 1 m asteroid 10 4 m planetesimal 10 6 m AU = average Earth-Sun separation

Star-Planet Distance [AU] Circularity Terrestrial Planet Formation

Giant Planet Formation Beyond the frost line, planetesimals can grow from rock and ice. This leads to the formation of “planetary cores”, which are rocky/icy planetesimals around 10x as massive as Earth. These cores are so massive that they accrete gas, forming gas giant planets.

Questions Where is the frost line in our Solar System? Between Earth and Mars? Between Neptune and Pluto? Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Is frost line around an M-dwarf at the same distance as the frost line around the Sun?

Kepler’s Laws 1 - Bodies orbit their parent star on elliptical orbits with the star at one focus of the orbit. 2 - In an orbit, the closer a body is to its parent star the faster it moves.

Kepler’s Laws 3 - The orbital period (P) of a body is related to the body’s average distance from its parent star (a) by the equation P 2 = a 3 (with P measured in years and a in AU). Bottom Line: Close-in planets have shorter orbital periods!

Electromagnetic Spectrum

Emission and Absorption Spectra Whether the spectrum is continuous, or in emission or absorption tells us about the composition and temperature structure of the object we are studying.

CO 2 Water

Questions of the Day What does it mean to say that we are made of star stuff? What are Kepler’s three laws? What is spectroscopy and how does it help us to learn about the Universe?

Quiz 1 - Explain two reasons why we limit our search for habitable planets to worlds around low-mass, main sequence stars. 2 - What three characteristics must a world have in order to be considered habitable? 3 - What is one thing you did not understand from today’s lecture?

A Multitude of Worlds 353 Planets 298 Planetary Systems 38 Multiple Planet Systems Over 92% of the planets discovered to date were found using the Radial Velocity (Doppler) technique. As of 7/21/09

Summary 1 - The Universe is a huge place and contains billions of trillions of stars (at least!). 2 - The life cycles of high-mass and low-mass stars are necessary for the production and distribution of the chemical elements of which life is made. 3 - Kepler’s Three Laws - orbits are ellipses - closer = faster - P 2 = a Extrasolar planets are detected by - radial velocity (indirect) - transit (indirect) - imaging (direct)

Extrasolar Planets - Doppler Technique The sound is at a higher pitch (smaller wavelength) as the car approaches and at a lower pitch (longer wavelength) as it recedes. The light waves are at a longer wavelength (redder) as the star moves away from you and at a shorter wavelength (bluer) as the star approaches you.

Extrasolar Planets - Doppler Technique Question How can we determine the planet-star separation?

Extrasolar Planets - Transit Technique We learn the size, mass and density of the planet!

Extrasolar Planets - Direct Detection 120 AU Mass of Neptune? Jupiter? Orbit of Neptune

Question Why are there so many close-in, Jupiter-mass planets?